Note: Descriptions are shown in the official language in which they were submitted.
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
1
Apparatus for Humidifying a Gas Flow
The present invention relates to apparatus for humidifying a
gas flow and including means for separating excess water
from the gas flow. The present invention is particularly
but not exclusively applicable for humidifying fuel gas and
oxidant gas used in a fuel cell for automotive purposes.
A known type of fuel cell has a polymer electrolyte membrane
in which hydrogen forming a fuel gas is passed over one side
of the membrane, the anode, where, in response to an applied
electrical load an electrochemical reaction takes place in
which hydrogen ions migrate through the membrane to combine
with oxidant, usually derived from air, on the other side,
or cathode, of the membrane. It is necessary for both the
hydrogen gas and the air, which are kept in separate
streams, to be humidified to ensure that a necessary
quantity of water passes through both sides of the fuel cell
where it serves to enhance the electrochemical action and
also to prevent the drying out of the membrane, which would
lead to poor efficiency in the electrochemical reaction and
damage, or at least a reduced service life, for the fuel
cell.
CA 02659517 2011-08-03
WO 2008/031442 PCT/EP2006/008904
2
German Patent No. DE 10028133 discloses apparatus
which is particularly suitable for humidifying a gas flow to
be used in a fuel cell system to humidify process gases. In
the specifications, the humidified device described
comprises three sections, a spray chamber, a heat exchanger
region, and a water separator. Water is injected in an
atomised form into the spray chamber where the atomised
water is mixed with the flow of the gas. In the heat
exchange region, heat exchange means are provided which
utilises the heat in the gas to at least partially evaporate
water to humidify the gas and to enable the excess water to
be at least partially condensed. In order to ensure that
satisfactory humidification takes place, a greater amount of
water is atomised than that which is theoretically required
to achieve a relative humidity of the gas of 100 percent.
The excess water is collected in a water collector or
separator located below the heat exchanger region.
The humidified device and water separator described have
disadvantages when used in an automotive application, in
particular, in coping with the g-forces which occur during
cornering and changes in angular position of the vehicle
when the vehicle is on a sloping surface, which can lead to
inefficient drainage and reduced water separation. Thus,
excess water can lie on the bottom of the separator where it
can be re-entrained by the gas flow and, in extreme
conditions, an excess of water can enter the fuel cell,
reducing its efficiency.
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
3
The present invention seeks to provide a humidifying
apparatus incorporating a water separator, which is much
less sensitive to g-forces than the known device.
According to the present invention there is provided a
device for humidifying a gas flow, including means for
supplying an atomised liquid and combining this with a gas
flow in a spray chamber to humidify the gas, passing the
combined atomised liquid and gas through a gas flow passage
which comprises a generally U-shaped passage having a first
generally vertical part through which the atomised liquid
and gas stream passes to a lower part, from where the gas
stream passes generally vertically upwardly to an outlet,
characterised in that the lower part of the passage
incorporates an opening through which excess water separated
out from the gas stream can pass to a water separator, the
opening being closable by float means, or includes a water
flow control valve which permits water to flow into the
chamber but substantially impedes water flow from the
chamber back into the gas flow passage.
Preferably, the float means controls a drain valve which
controls the flow of liquid out of the water separator. In
a preferred embodiment, the opening is at the lowermost part
of the gas flow passage and it is relatively small compared
to the cross-section of the passage and the cross-section of
the water separator chamber (reservoir). In this way, water
readily drains through into the water separator and reduces
the amount of water exposed to the gas flow for possible re-
entrainment. The water in the water separator is preferably
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
4
transferred for use elsewhere in the fuel cell operating
system for, for example, humidifying the incoming gas.
In another embodiment, the water separator chamber is
substantially square or rectangular in plan view having a
planar top wall which, in the installed condition on a
vehicle is substantially horizontal, four openings being
located adjacent that the four corners of the top wall, the
top wall defining the lower wall of the lowermost part of
the gas flow passage. Preferably, each of the four openings
includes a flow control valve incorporating a baffle to
restrict the flow of water in a direction from the chamber
to the gas passage.
A preferred embodiment of the present invention will now be
described by way of example with reference to the
accompanying drawings, in which:
Figure 1 shows in a cross-sectional view in schematic form
of a gas flow passage in a humidifier, together with a water
separator,
Figure 2 shows a side view of Figure 1,
Figures 3a 3b, and 3c show schematically in plan view, three
alternative layouts of single, double, and multi-outlet
designs of water separator,
Figure 4 shows a sectional side view of the embodiment of
Figure 3c, and
Figure 5 shows a detail view of a water flow control valve
used in the embodiment of Figures 3c and 4.
Figure 1 shows a gas flow passage 1 of a fuel gas
humidifier, together with a water separator 2. For further
CA 02659517 2011-08-03
WO 2008/031442 PCT/EP2006/008904
details of a fuel gas humidifier, attention is directed to
the aforementioned German Patent No. DE 10028133.
This specification discloses a spray chamber in which fuel
gas for a fuel cell, typically hydrogen, is mixed with
atomised water. The combined fuel gas and atomised water,
which consists of a large number of water droplets passes
through a heat exchanger, where the water droplets are
partially evaporated to humidify the gas and partially
condensed into water and larger water droplets.
In the present embodiment, the combined gas and atomised
water and the water droplets then pass through a generally
U-shaped flow passage, first passing downwardly through a
first generally vertically disposed gas flow passage section
3 to reach the lowermost part 4 of the passage 1 which
lowermost part is formed in a shaped section having inclined
sides 5 to reduce the cross-sectional area of the passage in
the downwardly vertical sense, the lowermost part
terminating in an opening 6 leading into the water separator
chamber 7. In the lowermost part 4 of the passage, the gas
flow is forced through a 180 degree turn to rise up an
outlet part 8 of the gas flow passage to an outlet 9 leading
to the input of a fuel cell. Thus, the opening 6 into the
water separator chamber 7 is relatively small compared to be
cross-section of the gas flow passage so that the
possibility of water droplets being re-entrained by the gas
flow is very much reduced. The opening 6 is generally on
the centreline of the water separator chamber 7 and is also
very much smaller than the cross-sectional area of the water
separator chamber to reduce the possibility of water in the
separator chamber re-entering the gas flow passage when the
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
6
vehicle's motion generates g-forces which disturb the water
in the chamber. The chamber may incorporate baffles to
reduce the tendency of the liquid in the chamber to surge
excessively.
Additionally, the efficiency of separating out the water
droplets from the humidified gas stream is increased because
the effect of gravitational forces tending to draw the water
droplets downwardly is increased by the reversal of the gas
flow, since the greater mass of the water droplets compared
to the gas increases the rate at which they drop out of the
gas, in the manner of a centrifugal separator.
The opening 6 from the gas flow passage into the water
separator 7 is controlled by a float 10 in the shape of a
ball which is adapted to close off the opening 6 if the
water level in the water separator rises above a
predetermined level. Should this occur, the float 10 also
may serve to operate a valve (not shown) which opens to
allow water to drain out of the separator. In normal
operation, the condensed water is drawn out of the water
separator by a pump and recirculated to humidify the
incoming fuel gas or oxidant supplied to be fuel cell.
The present design having the U-shaped gas flow passage with
the narrow opening to the water separator placed immediately
beneath enables the overall size and height of the
humidifier/water separator assembly to be much reduced
compared with the prior art referred to earlier. The design
also facilitates the draining of all water out of the system
so that the system is far less likely to be damaged by ice
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
7
formation when the vehicle is not in use under freezing
conditions. The use of floats to close the opening into the
water separator chamber has further advantages when water
from both sides of the fuel cell, that is the fuel gas side
and the airflow side can be vented into a common water
separator chamber. The use of the floats to close the
openings to the gas flow passages serves to prevent the two
different gases from entering the wrong passage from the
water separator chamber.
Referring now to Figure 2, in this arrangement two water
separator chambers 7a and 7b are provided spaced across the
lowermost part of the gas flow passage 4. In an alternative
form, as indicated by the dotted line 11, two flow passages
are provided side-by-side in a common housing, one of being
for the humidification of the fuel gas, the other for the
humidification of the air supply providing the oxidant for
the fuel cell. In this case, excess water in the process
gases on both sides of the membrane are vented into a common
water separator chamber.
Referring now to Figure 3, figure 3a shows the opening of a
single chamber water separator, figure 3b shows two openings
which lead into a common water separator chamber 7 although
they may lead into separate chambers, whilst figure 3c shows
an arrangement having four openings all opening into a
common water separator chamber 7.
Referring now to Figure 4, there is shown a sectional side
view of the embodiment shown in Figure 3 C. in which four
openings 6 all opening into a common water separator chamber
CA 02659517 2009-01-30
WO 2008/031442 PCT/EP2006/008904
8
7, are provided. The four openings are spaced apart towards
the four corners of the chamber 7 which is substantially
square or rectangular in plan. Instead of the closable
float valve 10 described in the embodiment of Figures 1 and
2, the openings in this embodiment each incorporate a water
flow control valve 13, further details of which are shown in
Figure 5. The control valves 13 have a venturi-shaped bore
having a centre section 14 of reduced diameter with tapered
inlet and outlet sections 15 and 16. The lower end of the
centre section adjacent to the chamber 7 has a flow-
restricting baffle 17 which has one or more bores of a
relatively small diameter. In this way, water impinging on
the top wall 18 of the chamber 7, which forms the lower wall
of the gas flow passage 3, can flow down through the control
valves but the baffle 17 serves to effectively prevent water
rising up back into the gas flow passage.
When the apparatus is installed in a vehicle, the wall 18 is
located substantially in a horizontal position. The use of
four flow control valves spaced apart ensures that whether
the vehicle is tilted laterally from one side to the other
or fore and aft, or is subjected to g-forces laterally or
fore and aft, any water separating out from the gas stream
will flow on to an area of the wall 18 containing an open
control valve so that the water can drain down into the
chamber 7. With this arrangement, it has been found that
although a degree of gas can pass into the chamber 7, this
does not affect the efficient functioning of the separator.
